Chainstitch conversion device for lockstitch sewing machines

ABSTRACT

A device for converting a lockstitch sewing machine into condition for forming single thread chainstitches, including a replacement throat plate with a thread engaging pin depending therefrom, and a thread deflecting member adapted to replace the bobbin in the sewing machine and formed with a radial arm arranged in cooperative relation with said thread engaging pin. The thread deflecting member is shiftably supported in the loop taker and arranged to be influenced only by the sewing thread for movement into and out of a position maintaining the sewing thread in engagement with the thread loop engaging pin.

United States Patent 11 1 Ivanko lM3lCh 13, 1973 [5 1 CHAINSTITCH CONVERSION DEVICE 3,194,197 7/1965 Ketterer et a1. ..112/168 FOR LOCKSTITCH SEWING 3,253,560 5/1966 Ketterer et al. ..112/168 MACHINES P E J R B I rzmary xammerames 0 er [75] Inventor. Michael F. Ivanko, Bloomsberg, Pa. Atwmey MarSha" J Breen et aL [73] Assignee: The Singer Company, New York,

N.(. [57] ABSTRACT [22] Filed: Nov. 23, 1971 A device for converting a lockstitch sewing machine into condition for forming single thread chainstitches,

[2]] Appl' 201514 including a replacement throat plate with a thread engaging pin depending therefrom, and a thread deflect- [52] US. Cl ..112/168, 112/202 ing member adapted to replace the bobbin in the sew- [51] Int. Cl. ..L ..D05b 1/14 irrg achine and formed with a radial arm arranged in of Search cooperative relation aid thread engaging The thread deflecting member is shiftably supported References Cited in the loop taker and arranged to be influenced only v UNITED S T PATENTS by the sewing thread for movement into and out of a position ma1nta1n1ng the sewrng thread 1n engagement 809,660 1/1906 Ammerman ..112/168 with the thread loop engaging pin. 3,173,390 3/1965 Bartosz ..ll2/l68 3,173,391 3/1965 Doerner ..112/168 2 Claims, 7 Drawing Figures CHAINSTITCH CONVERSION DEVICE FOR LOCKSTI'ICH SEWING MACHINES BACKGROUND OF THE INVENTION Prior chainstitch conversion devices for lockstitch sewing machines, such as those disclosed in the U.S. Pat. No. 3,173,390 Mar. 16, 1965 to F. J. Bartosz and U.S. Pat. No. 3,253,560, May 31, 1966 to S. J. Ketterer et al., utilize thread loop detaining elements which may be inserted in place on the conventional lockstitch forming instrumentalities. These prior chainstitching devices, however, require operative engagement of the thread loop detaining instrumentalities with operative mechanism of the sewing machine in order to control shift of the loop detaining elements into and out of effective position. As a result, the physical relationship of the conversion parts to the sewing machine stitch forming instrumentalities must be maintained at a very accurate degree, and the physical engagement of the operating parts gives rise to objectionably high noise levels during machine operation.

BRIEF SUMMARY OF THE INVENTION It is an object of this invention to provide chainstitch conversion fittings for a lockstitch sewing machine which may be operated successfully despite wide variations in the tolerances between the parts of the sewing machine to which the fittings are applied, and which may be operated without objectionably high noise levels. These objects and advantages are attained by an arrangement of conversion elements for chainstitch formation which do not require physical contact with any actuated part or element of the sewing machine, but rather utilize the sewing thread for the purpose of shifting the conversion parts alternately into and out of a position for detaining thread loops in the formation of chainstitches.

BRIEF DESCRIPTION OF THE DRAWINGS With the above and other objects and advantages in view, this invention is illustrated in the accompanying drawings of a preferred embodiment in which:

FIG. 1 represents a perspective view of a lockstitch forming loop taker together with fragments of the needle, throat plate, and bobbin thread pulloff element of a sewing machine to which the chainstitch conversion device of this invention has been applied,

FIG. 2 is a cross sectional view taken substantially along line 2-2 of FIG. 1 and showing the position of the parts as the thread loop is about to be released afterpenetration thereof by the needle,

FIG. 3 is a cross sectional view taken substantially along line 2-2 of FIG. 1 showing the thread loop detained by the chainstitch conversion fittings in readiness for penetration of the loop by the needle,

FIG. 4 represents a bottom plan view of the chainstitching throat plate,

FIG. 5 is a bottom plan view of the thread deflecting member of this invention.

FIG, 6 is a side elevational view thereof, and

FIG. 7 is a top plan view thereof.

In the drawings, 10 indicates a Iockstitch rotary loop taker formed with a loop. seizing beak 11 and preferably of the type arranged to rotate on a vertical axis substantially parallel to the path of endwise reciprocation of a thread carrying sewing machine needle 12. A bobbin case 13 is maintained stationary within the loop taker 11 by the constraining means (not shown) which may be of any conventional construction. The bobbin case 13 shown in the drawing is of a known type in which a pivoted hold-down arm 14 is carried on the bobbin case and provided with a depending projection 15 adapted to enter a central depression in a bobbin so as to hold in place and frictionally resist turning of a bobbin within the loop taker for the formation of lockstitches (Federal Stitch Type 301 The conversion device of this invention for changing a lockstitch sewing machine into a machine capable of forming single thread chainstitches (Federal Stitch Type 101) includes a replacement throat plate 20 for chainstitching. The chainstitching throat plate 20 is similar to a throat plate usable for the formation of lockstitches in that it includes apertures 21 to facilitate securing the throat plate in place, slots 22 to accommodate a work feed dog 23, and an overall shape identical with the conventional throat plate. The chainstitching throat plate 20 differs from the throat plate usable for lockstitches in that an aperture 24 through which the needle penetrates is elongated in the direction of the feed dog slots 22. Another difference of the chainstitching throat plate 20 in comparison with a Iockstitch forming throat plate is the provision of a depending thread engaging pin 25 projecting therefrom. Preferably, as shown in FIGS. 2 and 3 the thread engaging pin is formed with a slabbed portion 26 at the free extremity thereof.

The chainstitch conversion device of this invention also includes a thread loop deflecting member indicated generally at 30 which is adapted to be substituted in the bobbin case 13 in place of a bobbin which would be required for the formation of lockstitches. The thread loop deflecting member take the form of a disk formed with a central depression 31 adapted to accommodate the projection 15 of the bobbin hold-down arm 14 which thus serves to constrain the thread loop deflecting member in place in the bobbin case. A radial arm 32 is formed on the thread loop deflecting member which fits between the arms of the work feed dog and extends beneath the thread engaging pin 25 on the chainstitching throat plate 20. The arm 32, serves to direct thread loops onto the thread engaging pin 25 and to regulate the release of loops of thread from the thread engaging pin. The radial arm 32 is preferably formed with a shallow recess 33 which provides a seat into which the thread engaging pin 25 is accommodated.

As shown in FIGS. 5 and 6, the thread loop deflecting member 30 is formed with a depending annular flange 35 which projects within the bobbin case when the thread loop deflecting member is positioned therein and serves to prevent needle thread loops from snagging parts of the bobbin case as the thread loops are being influenced by the thread loop deflecting member. Depending beneath the thread loop deflecting member exteriorly of the depending annular flange 35 is a pair of fulcrum projections 36 which as shown in FIG. 6 are located between the central depression 31 and the radial arm 32 of the thread loop deflecting member. The fulcrum projections define an axis X-X for rocking movement of the thread loop deflecting member 30 relatively to the bobbin case 13, which axis is spaced the distanced indicated at Y in FIG. 6 from the central depression 31 in the direction of the radial arm 32.

In the absence of any other external forces being applied to the thread loop deflecting member, therefore, the hold-down arm 14 will apply downward pressure on the opposite side of the axis X-X on the thread loop deflecting member from the radial arm 32 and will thus bias the radial arm upwardly against the thread engaging pin 25. Any thread loop which is engaged by the loop seizing beak ll of the loop taker will thus be directed by the thread loop deflecting member onto the thread engaging pin 25 as shown in FIG. 3.

Illustrated in FIGS. 1, 2 and 3 is a thread pull-off member 40 which is conventional in lockstitch sewing machines where it serves to draw off bobbin thread during stitch formation so as to promote uniformity in lockstitch formation. The thread pull-off member may be formed as a lever 41 pivoted as at 42 to the machine frame and provided with a needle accommodating aperture 43. The thread pull-off device may include a return spring 44 which biases a follower projection 45 on the lever against the underside of the feed dog 23 as shown in FIG. 3. The outer rim portion 46 of the needle aperture in the thread pull-off member provides the active pull-off element which influences the sewing threads. When the feed dog 23 is lowered as shown in FIG. 2, the follower projection 45 in contact with the feed dog causes the thread pull-off member also to be lowered and the thread T which has been carried through the needle aperture 43 in the thread pull-off member will be drawn downwardly with it by the outer rim portion 46. This downward pull exerted on the thread loop which is detained on the thread engaging pin 25 will exert a downward force on the radial arm 32 of the thread loop deflecting member 30. When the thread loop deflecting member is thus drawn downwardly moving the bottom of the recess 33 away from the thread engaging pin 25, a passageway is provided therebetween through which the thread loop will be released from the thread engaging pin and will be freed therefrom so that it may be drawn first onto the needle and then upwardly into the stitches being formed in work fabrics W the next time the needle is raised. Preferably, the recess 33 in the radial arm 32 of the thread loop deflector is sufficiently deep that it cannot move completely out of engagement with the thread engaging pin 25. In this way, the pin 25 provides restraint against rotation of the thread loop deflector 30.

As indicated in FIG. 2 the release of the thread loops from the thread engaging pin 25 takes place while the feed dog is lowered which corresponds in time to that portion of each stitch forming cycle when the needle occupies the position penetrating the work fabrics W. The thread loops will be released from the thread engaging pin 25, therefore, only after the needle has penetrated the loop and, therefore, a continuing chain of thread loops will be formed.

Since the forces necessary to cause rocking of the thread loop deflecting member 30 are imparted by the thread T, any engagement of operative working parts of the sewing machine with the thread loop deflecting member 30 is obviated, and thus an exceedingly quiet operation is attained with the device of this invention.

Having set forth the nature of this invention, what IS claimed herein is:

l. A chainstitch conversion device for a lockstitch sewing machine having a thread carrying needle, a rotary loop taker journaled on an axis perpendicular to and beneath a throat plate which is formed with a needle aperture and feed dog accommodating slots, and a bobbin accommodating case constrained against rotation in said loop taker and provided with a bobbin holddown arm downwardly biased and formed with a projection disposed for engagement with the center of the bobbin in the bobbin case, said chainstitch conversion device comprising a chainstitching throat plate adapted to replace the conventional throat plate, said chainstitching throat plate being formed with a depending thread engaging pin located in front of the needle aperture, and a thread loop deflecting member adapted to replace the bobbin in the bobbin case of said loop taker, said thread loop deflecting member comprising a disk formed with a central depression accommodating said bobbin hold-down arm projection, a radial arm projecting from said thread loop deflecting member and underlying said thread engaging pin depending from said chainstitching throat plate, and fulcrum projections depending from said thread loop deflecting member pivotally supporting said thread loop deflecting member for rocking movement relatively to said bobbin case, said fulcrum projections being located between said central depression and said radial arm on said thread loop deflecting member.

2. A chainstitch conversion device for a lockstitch sewing machine as set forth in claim 1 in which a thread pull-off element is shiftably supported for movement toward and away from the throat plate in a path between the path of said needle and the thread engaging pin depending beneath said chainstitch throat plate, and in which said thread loop deflecting member is maintained in spaced relationship with said thread pulloff element. 

1. A chainstitch conversion device for a lockstitch sewing machine having a thread carrying needle, a rotary loop taker journaled on an axis perpendicular to and beneath a throat plate which is formed with a needle aperture and feed dog accommodating slots, and a bobbin accommodating case constrained against rotation in said loop taker and provided with a bobbin hold-down arm downwardly biased and formed with a projection disposed for engagement with the center of the bobbin in the bobbin case, said chainstitch conversion device comprising a chainstitching throat plate adapted to replace the conventional throat plate, said chainstitching throat plate being formed with a depending thread engaging pin located in front of the needle aperture, and a thread loop deflecting member adapted to replace the bobbin in the bobbin case of said loop taker, said thread loop Deflecting member comprising a disk formed with a central depression accommodating said bobbin hold-down arm projection, a radial arm projecting from said thread loop deflecting member and underlying said thread engaging pin depending from said chainstitching throat plate, and fulcrum projections depending from said thread loop deflecting member pivotally supporting said thread loop deflecting member for rocking movement relatively to said bobbin case, said fulcrum projections being located between said central depression and said radial arm on said thread loop deflecting member.
 1. A chainstitch conversion device for a lockstitch sewing machine having a thread carrying needle, a rotary loop taker journaled on an axis perpendicular to and beneath a throat plate which is formed with a needle aperture and feed dog accommodating slots, and a bobbin accommodating case constrained against rotation in said loop taker and provided with a bobbin hold-down arm downwardly biased and formed with a projection disposed for engagement with the center of the bobbin in the bobbin case, said chainstitch conversion device comprising a chainstitching throat plate adapted to replace the conventional throat plate, said chainstitching throat plate being formed with a depending thread engaging pin located in front of the needle aperture, and a thread loop deflecting member adapted to replace the bobbin in the bobbin case of said loop taker, said thread loop Deflecting member comprising a disk formed with a central depression accommodating said bobbin hold-down arm projection, a radial arm projecting from said thread loop deflecting member and underlying said thread engaging pin depending from said chainstitching throat plate, and fulcrum projections depending from said thread loop deflecting member pivotally supporting said thread loop deflecting member for rocking movement relatively to said bobbin case, said fulcrum projections being located between said central depression and said radial arm on said thread loop deflecting member. 